The present invention relates to multi-pen graphics plotter and, more particularly, in a multi-position graphics plotter pen carousel system employing a pen capping mechanism therein at each pen position for capping and uncapping pens held by the carousel, to the improvement for allowing the sensing of pen presence at the pen positions and the indexing of the carousel with a single sensor comprising, each pen capping mechanism assuming a first position with a pen in the pen position and assuming a second position with no pen in the pen position; a plurality of first sensible means associated with respective ones of the pen capping mechanisms for exhibiting a first characteristic when a pen is contained at the associated pen position and for exhibiting a second characteristic when no pen is contained at the pen position; a plurality of second sensible means associated with respective ones of the pen positions for constantly exhibiting the first characteristic; sensor means for sensing the first and second characteristics and for developing a sensible signal at an output thereof indicating whether the first or second characteristic is presently being sensed; means for positioning the sensor means to sense the first sensible means and for stepping the carousel between respective ones of the first sensible means when sensing pen presence with the sensor means; and, means for positioning the sensor means to sense the second sensible means and for stepping the carousel between respective ones of the second sensible means when indexing the carousel with the sensing means whereby the sensible signal at the output of the sensor means indicating the first characteristic indicates the presence of a pen at a pen position of the carousel when sensing the first sensible means and indicates the passage of a pen position when sensing the second sensible means to count pen positions to index the carousel.
In the field of graphics plotters, the use of a pen carousel for containing a plurality of pens of different types to be employed within the plotting process is popular. Typically, the carousel is removable so that different pen types can be employed by simply removing and replacing the carousel. Such a prior art pen carousel is shown in FIGS. 1 and 2. The carousel 10 comprises a hollow cylindrical body 12 with a hub 14 extending concentrically upward from the top thereof. The hub 14 is adapted to be placed over and lockingly mated with a spindle which is rotated, in turn, to turn the carousel 10 in the performance of its functions. The body 12 has a plurality of equally spaced gripping fingers 16 each adapted to releasably hold a pen 18 for transfer to a penholding mechanism (not shown) which accomplishes the actual drawing employing a pen 18 selected from the carousel 10. Employing the carousel 10, the plotter logic can, at run-time, select from a multitude of different pen tip sizes, types, and ink colors in the creation of the drawing being plotted.
In employing a pen carousel such as 10 of FIGS. 1 and 2, there are two sensing requirements as indicated in the drawings which, heretofore, have been separately accomplished in the mechanism. First, as depicted in FIG. 1, there must be some means for sensing whether or not a selected pen position on the carousel 10 is presently holding a pen 18; that is, at run-time, if pen #5 is selected and the drawing mechanism mechanicaly affects a transfer of a non-existent pen from position #5, the plot will continue without drawing lines for that portion requiring pen #5. Accordingly, a typical prior art approach is to have a reflective surface on the pens 18 from which a light beam 20 from a source 22 will be reflected to a detector 24 when a pen 18 is present in the particular position being sensed. A signal on the output line 26 from the detector 24 can then be employed by the plotter logic to determine whether or not a pen is present. Obviously, without a pen 18 in the associated gripping finger 16, the light beam 20 is not reflected and no signal is developed in detector 24.
The second sensing requirement is depicted in FIG. 2. That is, when pen #5 is selected, which of the plurality of pens 18 is pen #5?. To make this determination, a plurality of equally spaced slots 28 are provided through the sidewalls of the body 12 with one slot 28 for each pen position. A second light source 30 is placed on one side of the sidewalls 32 of the body 12 and a second detector 34 is positioned opposite it on the other side of the sidewall 32 in line with the path of the slots 28 as the carousel 10 is rotated. Accordingly, the light beam 20 from the light source 30 to the detector 34 is interrupted by the sidewalls 32 and allowed to pass by the slots 28. Thus, by starting from a known position and counting the slots 28 associated with the respective positions 18 any desired pen can be found by the plotter logic.
As will be appreciated, the above-described prior art approach requires two sets of light sources and detectors as well as specially equipped pens adapted for the particular sensing system being employed. This is both inconvenient, more complex, and more costly.
Wherefore, it is the object of the present invention to provide a pen carousel providing the ability to sense pen presence and indexing positions with a single set of sensors.
It is another object of the present invention to permit pen sensing in a pen carousel in a manner which does not require pens with special provision for being sensed.
Other objects and benefits of the present invention will become apparent from the description contained hereinafter taken in conjunction with the descriptive drawings thereof.